Vacuum gas oil (VGO) is a hydrocarbon stream recovered from one or more petrochemical refinery unit operations typically as a side cut from a vacuum column, a crude column and/or a coker column and contains sulfur, nitrogen, and other impurities. VGO can include, for example, light vacuum gas oil, heavy vacuum gas oil, heavy coker gas oil, light coker gas oil, and/or heavy atmospheric gas oil. Prior to treating to upgrade the oil, VGO comprises a range of various hydrocarbons (e.g., paraffins, olefins, naphthenes, aromatics with various molecular weights) with different boiling points at atmospheric pressure including a VGO range hydrocarbon fraction and a diesel range hydrocarbon fraction. For example, untreated VGO (e.g., VGO feedstock for treating) can have an initial boiling point (IBP) of from 270 to 350° C. and a final boiling point (FBP) of from 500 to 580° C. in which the VGO range hydrocarbon fraction has an IBP of from 330 to 360° C. and a FBP of from 500 to 580° C. and the diesel range hydrocarbon fraction has an IBP of from 270 to 300° C. and a FBP of from 360 to 400° C.
To remove sulfur, nitrogen and the other impurities and to generally upgrade the oil, VGO is hydrotreated and fractionated to form various hydrotreated effluent product streams that include a VGO product draw stream and a diesel product draw stream. The hydrotreated effluent product stream(s) can then be further treated downstream, for example, by a catalytic cracking process to convert and/or further upgrade the stream(s) to higher value refinery products. Unfortunately, the diesel product draw stream from hydrotreating and fractionating is a relatively low value diesel product having a corresponding relatively low cetane number(s). In particular, a cetane number is a measure of the combustible quality of diesel fuel during compression ignition. Higher cetane numbers (e.g., 52 or greater) correspond to higher value diesel products than diesel products having lower cetane numbers. Additionally, during catalytic cracking process of hydrotreated VGO, the resulting diesel range hydrocarbons typically known as light cycle oil (LCO) are still of relatively low value.
Accordingly, it is desirable to provide apparatuses and methods for treating a VGO feed that comprises primarily VGO and diesel range hydrocarbons to recover a VGO product and a relatively high cetane number diesel product. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background.